A. Field of the Invention
The present invention relates generally to blood substitutes and, more particularly, to a carbide-derived-carbon hemoglobin-based oxygen carrier (CDC HBOC) and a carbide-derived-carbon oxygen carrier (CDC OC).
B. Description of the Related Art
Blood loss is the primary cause of preventable civilian trauma related death (Hoyt et al., 1994; Sauaia et al., 1995), with trauma being the leading cause of death for ages 1-34 (Bonnie et al., 1999; Holcomb, 2004). Approximately 80% of trauma related civilian deaths and combat casualty fatalities result not from the initial injury but the associated exsanguination and hemorrhagic shock (Hoyt et al., 1994; Bellamy, 1984; Champion et al., 2003). A decrease in oxygenation capacity as a result of blood loss, in addition to hypovolemia, contributes to the observed high mortality rates (Muir, 2006).
The transfusion of whole blood or packed red blood cells (pRBCs) requires that blood be type matched and free of pathogens such as HIV and hepatitis. At the same time, RBCs are only stable for approximately 42 days at 4° C. and cannot be sterilized and thus are impractical on the front-lines or extended natural disaster scenarios (Winslow, 2003). Indeed, RBCs and pRBCs are known to decrease in effectiveness in as little as five days (Keidan et al., 2004). The ever increasingly limited availability of fresh, pathogen free, human blood products for transfusion in emergency and non-emergency situations has led to the development of hemoglobin-based oxygen carriers (HBOCs) (Winslow, 2003; Lowe, 2006a, 2006b; Stollings and Oyen, 2006; Moore et al., 2006; Alayash et al., 2007).
HBOCs have undergone several developmental generations since research first began on blood substitutes in the early 1900s (Winslow, 2003; Sellards and Minot, 1916). Toxicity effects due to hemoglobin extravasation, glomerular filtration rates, and NO redox chemistry have proven to be a major hurdle for the clinical application of HBOCs (Dunne et al., 2006; Beuhler and Alayash, 2004; D'agnillo and Alayash, 2000; Bonaventura et al., 2007; Tsai et al., 2006). Monomeric or non-crosslinked hemoglobins dissociate and lead to nephrotoxicity. Monomeric, dimeric, and small polymeric HBOCs are too small to remain in the laminar flow of small blood vessels and therefore can approach or extravasate into the vascular endothelia and react with NO resulting in vasoconstriction, and the high colloid osmotic pressure and blood viscosity from HBOCs affect blood flow and sheer stress on the vasculature (Buehler and Alayash, 2004).
In addition to the need for HBOCs in cases of blood loss, countless numbers of patients suffer from chronic wounds such as diabetic ulcers or various forms of necrotizing fasciitis that often develop from the body's inability to sufficiently oxygenate damaged or poisoned tissues (Young et al., 2006; Strauss, 2005). Chronic foot ulcers affect 4-10% of the diabetic population resulting in 50-80% of all lower extremity amputations (Lavery et al., 1996, Boulton, 1995; Reiber, 1996). These conditions are often relieved through amputation, surgical intervention, and/or hyperbaric oxygen treatment, which are invasive or not commonly available and expensive. These could be replaced with a simple, localized, topical oxygenating treatment (Young et al., 2006, Widjaja et al., 2005, Fife et al., 2007, Gill and Bell, 2004; Jallali et al., 2005).
Tissue engineering and tissue regeneration require controlled and sustained oxygenation for optimal growth and function. The lack of sufficient oxygen diffusion is one of the greatest current hurdles in tissue engineering and limits the size of tissues that can be regenerated or engineered (Harrison et al., 2007; Khademhosseini et al., 2007). Adequate, targeted, oxygen delivery to hypoxic or injured tissues via hemoglobin-based oxygen carriers (HBOCs), either in vivo or in vitro, is crucial to accelerate wound healing and tissue regrowth, delay or prevent the onset of necrosis, and decrease the mortality rate of trauma patients.
There is an additional and increasing need for HBOCs to extend the biological capabilities of emergency responders and war fighters beyond current physiological capacity under extenuating and harsh environmental circumstances that often lead to exhaustion, hypoxia, hypothermia, and death. Altitudinal PO2 levels vary from ˜160 mmHg at sea level to only ˜95 mmHg at 4000 m, which is the typical altitude of the Hindu Kush mountain range passes on the border of Afghanistan and Pakistan. The brain is the organ most dependent on blood oxygen levels, and consumes ˜20% of available oxygen (Erekińska and Silver, 2001). Thus, the initial effects of hypoxia and hypothermia often lead to confusion and loss of consciousness, impeding emergency rescue results and military operational success (Erekińska and Silver, 2001, Rossen et al., 1943). Emergency rescue efforts and military operations can be enhanced by the ability to undergo substantial hypoventilation/submersion, or extreme physical activity without exhaustion for extended periods of time, all aided by tissue oxygenation from intelligent HBOCs. Moreover, US military response to developing situations in demanding high-altitude arenas is hampered by the necessity to acclimate war fighters, sometimes for weeks, before deployment (Muza, 2007). The ability to rapidly increase potential oxygenation, in preparation for or in response to extensive physical activity, hypoxia, or hypothermia, is of paramount importance to emergency first responders and war fighter deployment.
The need for controlled and targeted oxygenation of tissues, either in vivo (trauma, stroke, ischemia, hypoxia, hypothermia, wound healing, fatigue) or in vitro (tissue engineering), has instigated substantial research efforts to develop blood substitutes, consisting of both volume expanders and oxygen therapeutics. Hemoglobin-based oxygen carriers (HBOCs) have great potential over other oxygen delivery methods, such as perfluorocarbons or silicone oils, to deliver oxygen because of their biocompatibility and inherent sensitivity to physiological changes in oxygen partial pressure (PO2) necessary for O2/CO2 exchange and respiration.
Much progress has recently been made in the field of HBOCs; however, despite more than 30 years of research and several design iterations, HBOCs still suffer from stability and toxicity related issues resulting from the NO scavenging and redox associated side-reactions of an acellular heme group and over-oxygenation of normoxic tissues (Natanson et al., 2008; Winslow et al., 2003). A stable, biocompatible (non-toxic), tunable HBOC system that indefinitely sequesters the hemoglobin from the vasculature and intelligently responds to physiological cues to specifically deliver oxygen to hypoxic/ischemic tissues only where and when required is urgently required.
Current HBOC technology typically relies on (i) manipulations of human or bovine hemoglobin (e.g. stroma free, cross-linked, polymerized, and chemically modified) and (ii) encapsulation of such for delivery by a variety of methods including liposomes, silica particles, hydrogels, and polymerization. Human or bovine hemoglobin has traditionally been used in these research efforts because of its ease of access and non-immunogenicity in a human system. Many of the current encapsulation technologies result from pharmaceutical and drug delivery research, in which the formulation slowly dissolves to deliver the enclosed payload at a specified rate. When using this type of delivery platform, other hemoglobin variants, which might provide improved oxygen delivery profiles, often have not been used out of immunogenicity/toxicity concerns. Due to the toxicity of the acellular heme group, no HBOCs have heretofore been available for clinical use, beyond compassionate care, in the United States (June 2008).
Recent reviews of the current HBOC treatments under production or recently involved in clinical studies reveal a significant increase in the rate of death, myocardial infarction, hypertension, and renal toxicity (Natanson et al., 2008; Buehler and Alayash, 2004; D'agnillo and Alayash, 2000; Bonaventura et al., 2007). It is gravely apparent that given the dire need for life-saving blood substitutes and the toxicity of the current methodologies, a new pathway toward effective HBOCs must be pursued.
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.